Converter lens device and photographing system including the same

ABSTRACT

The present disclosure is directed to a converter lens device that includes a first mount to which a master lens device is capable of being attached, a second mount to which a camera body is capable of being attached and a converter lens having a negative refractive power, wherein, an optical system comprising the converter lens device and the master lens device has a focal length longer than a focal length of an optical system of the master lens device, the converter lens comprises sequentially from an object side, a first lens unit of a positive refractive power, a second lens unit of a negative refractive power, and a third lens unit.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is based upon and claims the benefit of priorityfrom the prior Japanese Patent Application No. 2015-055954 filed on Mar.19, 2015; the entire contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a converter lens device for an opticalsystem having a focal length longer than a focal length of an opticalsystem of a master lens device, and to a photographing system includingsuch a converter lens device.

Description of the Related Art

A converter lens is known as an optical system for changing the focallength of a master lens. In application, the converter lens is attachedto an object side of the master lens or an image side of the masterlens. The converter lens attached to the image side of the master lensis called a rear converter lens.

A converter lens device including a rear converter lens includes twomounts. One of the mounts is a mount associated with a mount of a masterlens device, and the other mount is a mount associated with a mount of acamera body.

In application of the converter lens device, the converter lens deviceis disposed between the master lens device and the camera body such thateach of the two mounts is interposed between the converter lens deviceand the master lens device or the camera body. In this manner, the focallength of the master lens can be changed. A rear converter lens forincreasing the focal length of a master lens is called a rearteleconverter lens.

The focal length of the master lens can be increased. For this reason,rear teleconverter lenses are used for users of single-lens reflexcameras with interchangeable lenses, especially users who performtelephotographing.

A camera system not using a quick return mirror, that is, a camerasystem whose size and thickness are reduced by reducing a flange focaldistance, has been known. For such a camera system, a rear teleconverterlens is also demanded.

SUMMARY OF THE INVENTION

A converter lens device according to the present invention includes:

-   -   a first mount part to which a master lens device is attached;    -   a second mount part to which a camera body is attached; and    -   a converter lens having a negative refractive power, wherein,    -   an optical system constituted by the converter lens device and        the master lens device has a focal length longer than a focal        length of an optical system in the master lens device,    -   the converter lens includes sequentially from an object side,    -   a first lens unit having a positive refractive power,    -   a second lens unit having a negative refractive power, and    -   a third lens unit, and        where    -   the object side is a side closer to the first mount part, an        image side is a side closer to the second mount part.

A photographing system according to the present invention includes:

-   -   a master lens device;    -   a camera body including an image pickup sensor; and    -   a converter lens device attachable between the master lens        device and the camera body,    -   an optical system constituted by the master lens device and the        converter lens device forms an image of an object,    -   the image pickup sensor is disposed at an image position of the        object and converts an image of the object into an electric        signal, and    -   the converter lens device includes one of the above-described        converter lenses.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a lens cross sectional view of a converter lens according toExample 1.

FIG. 2 is a lens cross sectional view of a converter lens according toExample 2.

FIG. 3 is a lens cross sectional view of a converter lens according toExample 3.

FIG. 4 is a lens cross sectional view of a converter lens according toExample 4.

FIG. 5 is a lens cross sectional view of a converter lens according toExample 5.

FIG. 6 is a lens cross sectional view of a converter lens according toExample 6

FIG. 7A, FIG. 7B, FIG. 7C, and FIG. 7D show aberrations of the converterlens according to Example 1, specifically a spherical aberration (SA),an astigmatism (AS), a distortion (DT), and a magnification chromaticaberration (CC).

FIG. 8A, FIG. 8B, FIG. 8C, and FIG. 8D show aberrations of the converterlens according to Example 2, specifically a spherical aberration (SA),an astigmatism (AS), a distortion (DT), and a magnification chromaticaberration (CC).

FIG. 9A, FIG. 9B, FIG. 9C, and FIG. 9D show aberrations of the converterlens according to Example 3, specifically a spherical aberration (SA),an astigmatism (AS), a distortion (DT), and a magnification chromaticaberration (CC).

FIG. 10A, FIG. 10B, FIG. 10C, and FIG. 10D show aberrations of theconverter lens according to Example 4, specifically a sphericalaberration (SA), an astigmatism (AS), a distortion (DT), and amagnification chromatic aberration (CC).

FIG. 11A, FIG. 11B, FIG. 11C, and FIG. 11D show aberrations of theconverter lens according to Example 5, specifically a sphericalaberration (SA), an astigmatism (AS), a distortion (DT), and amagnification chromatic aberration (CC).

FIG. 12A, FIG. 12B, FIG. 12C, and FIG. 12D show aberrations of theconverter lens according to Example 6, specifically a sphericalaberration (SA), an astigmatism (AS), a distortion (DT), and amagnification chromatic aberration (CC).

FIG. 13 is a lens cross sectional view of a master lens.

FIG. 14 is a lens cross sectional view showing a combination of a masterlens and a converter lens.

FIG. 15 is a cross sectional view of a photographing system,specifically a cross sectional view in which a master lens device and aconverter lens device are attached to a camera.

DETAILED DESCRIPTION OF THE INVENTION

Prior to description of examples, advantages of an embodiment in anaspect of the present invention will be described. Advantages of theembodiment will be described using specific illustrations. However,similarly to the cases of examples below, the illustrated aspect ismerely part of aspects included in the present invention, and there area large number of variations of the aspect. Thus, the present inventionis not limited to the illustrated aspect.

A converter lens according to the present embodiment will be described.In the following description, an object side is a side closer to a firstmount, and an image side is a side closer to a second mount. A masterlens device can be disposed at the object side, and a camera body can bedisposed at the image side.

A converter lens device can include: a first mount to which a masterlens device is attached; a second mount to which a camera body isattached; and a converter lens having a negative refractive power. Anoptical system constituted by the converter lens device and the masterlens device can have a focal length longer than a focal length of anoptical system in the master lens device. The converter lens can includesequentially from an object side, a first lens unit having a positiverefractive power, a second lens unit having a negative refractive power,and a third lens unit.

A converter lens in a converter lens device according to the presentembodiment (hereinafter referred to as a “converter lens of the presentembodiment”) functions as a rear converter lens. Thus, in use, theconverter lens device can be sandwiched between a master lens device anda camera body. To obtain this configuration, the converter lens devicecan include a first mount and a second mount. The first mount can be amount to which the master lens device is to be attached. The secondmount can be a mount to which the camera body is to be attached.

The converter lens of the present embodiment can function as ateleconverter lens. Thus, an optical system constituted by the converterlens device and the master lens device can have a focal length longerthan a focal length of an optical system in the master lens device.

The converter lens of the present embodiment can include sequentiallyfrom an object side, a first lens unit, having a positive refractivepower, a second lens unit having a negative refractive power, and athird lens unit. This configuration can enable the first lens unit andthe second lens unit to reduce a spherical aberration and a comaaberration.

Since the second lens unit has the negative refractive power, amagnification of the converter lens can be obtained although theconverter lens is disposed in a small space between the master lensdevice and the camera body. The magnification of the converter lens canbe 1.4 times or more. The magnification of the converter lens also canbe 1.7 times or more or 2.0 times or more.

A converter lens device according to a first embodiment has the basicconfiguration described above and can satisfy conditional expression(1):0.1≦|f|/(β×D)≦0.87  (1)wherein

-   -   f is a focal length of the converter lens,    -   β is a magnification of the converter lens, and    -   D is a thickness of the converter lens on an optical axis.

Conditional expression (1) is a conditional expression defining thefocal length of the converter lens. The converter lens of the presentembodiment is a converter lens applicable to a camera system having arelatively short flange focal distance. Thus, in the converter lens ofthe present embodiment, the refractive power of each lens unit can belarge, and in view of this, aberrations need to be reduced.

However, if the number of lenses is increased in order to reduceaberrations, the total length of the converter lens can increase. Inview of this, the converter lens device of the present embodiment isconfigured to satisfy conditional expression (1), thereby reducing thetotal length of the converter lens and obtaining a relatively largemagnification.

A desired magnification can be obtained by avoiding values above theupper limit of conditional expression (1). Aberrations can be reduced byavoiding values below the lower limit of conditional expression (1).

A converter lens device according to a second embodiment has a similarconfiguration as the embodiment described above. The second embodimentis in a configuration in which the second lens unit can includesequentially from the object side, an object side lens sub-unit having anegative refractive power, and an image side lens sub-unit having anegative refractive power, and can satisfy conditional expression (2):1.7≦f ₂₁ /f ₂₂≦18  (2)where

-   -   f₂₁ is a focal length of the object side lens sub-unit, and    -   f₂₂ is a focal length of the image side lens sub-unit.

In the converter lens device of the present embodiment, the second lensunit can be divided into the object side lens sub-unit and the imageside lens sub-unit disposed in this order from the object side, and eachof the lens sub-units can have the negative refractive power. With thisconfiguration, even in a configuration in which the second lens unit hasa relatively large negative refractive power, the refractive power canbe dispersed to the two lens sub-units, and thus, a spherical aberrationand a coma aberration occurring in each lens surface in the second lensunit can be reduced with a desired magnification maintained.

Even in a configuration in which the second lens unit has a relativelylarge refractive power as a whole, the refractive power of the objectside lens sub-unit and the refractive power of the image side lenssub-unit do not increase. Thus, effects on eccentricity can be reduced.Specifically, even when eccentricity occurs in a lens during assembly ofthe object side lens sub-unit, degradation of aberrations can besuppressed. Similar advantages can be obtained for the image side lenssub-unit.

In addition, even when eccentricity occurs between the object side lenssub-unit and the image side lens sub-unit during assembly of the secondlens unit, degradation of aberrations in the second lens unit can besuppressed. As described above, since the second lens unit constitutedby the two lens sub-units has a relatively large allowance foreccentricity, assembly performance of the second lens unit can beenhanced.

Furthermore, the second lens unit constituted by the two lens sub-unitscan reduce the refractive power of each surface of lenses constitutingthe second lens unit. Thus, occurrence of unwanted light such as ghostscan be suppressed. The second lens unit constituted by the two lenssub-units is effective especially for suppressing occurrence of ghostsin the surface of the image side lens sub-unit closest to the imageside.

In this manner, the second lens unit constituted by the two lenssub-units can obtain good aberration reduction, enhance assemblyperformance of the optical system, and suppress occurrence of ghosts.

The converter lens device of the present embodiment can satisfyconditional expression (2) described above.

An excessive increase in the refractive power of the image side lenssub-unit can be prevented, by avoiding values above the upper limit ofconditional expression (2). In this manner, reduction of advantagesobtained by the second lens unit constituted by the two lens sub-unitscan be prevented.

An excessive increase in the refractive power of the object side lenssub-unit can also be prevented by avoiding values below the lower limitof conditional expression (2). In this manner, reduction of advantagesobtained by approaching the principal point toward the object side canbe prevented. In this case, since the refractive power of the converterlens does not increase, aberrations can be reduced with a limited numberof lenses.

A converter lens device according to a third embodiment hasconfiguration similar configuration to the embodiments described above.The third embodiment is in a configuration in which the second lens unitcan include sequentially from the object side, an object side lenssub-unit having a negative refractive power, and an image side lenssub-unit having a negative refractive power, and each of the object sidelens sub-unit and the image side lens sub-unit can include a cementedlens, and can satisfy conditional expression (2′):0.6≦f ₂₁ /f ₂₂≦10  (2′)where

-   -   f₂₁ is a focal length of the object side lens sub-unit, and    -   f₂₂ is a focal length of the image side lens sub-unit.

As described above, the second lens unit constituted by the two lenssub-units can reduce a spherical aberration and a coma aberrationoccurring in each lens surface in the second lens unit, can reduceinfluences on eccentricity (enhance assembly performance of the opticalsystem), and can suppress occurrence of ghosts.

In particular, in a configuration in which the second lens unit has alarge negative refractive power, it can be difficult to accuratelydetermine the relative position with the first lens unit, and thus,difficulty in assembly can increase. In addition, since a comaaberration is reduced the first lens unit and the second lens unit,occurrence of an error in determining the relative position can lead todeterioration of performance of a peripheral portion. In view of this,the second lens unit can be divided into the object side lens sub-unitand the image side lens sub-unit.

Furthermore, since the refractive power of each lens surface can bereduced, the second lens unit constituted by the two lens sub-units canbe also advantageous for reducing occurrence of unwanted light such asghosts. The second lens unit constituted by the two lens sub-units canbe effective for suppressing occurrence of ghosts in the surface of theimage side lens sub-unit closest to the image side.

Moreover, since the object side lens sub-unit can include the cementedlens, differences in a spherical aberration and a coma aberrationdepending on the wavelength can be reduced. In addition, since the imageside lens sub-unit can include the cemented lens, processability andassembly performance of the image side lens sub-unit can be enhanced.

The converter lens device of the present embodiment can satisfyconditional expression (2′) described above. Technical significance ofconditional expression (2′) can be similar to that of conditionalexpression (2).

A converter lens device according to a fourth embodiment can have asimilar configuration as those embodiments described above. The fourthembodiment is of a configuration in which the second lens unit caninclude sequentially from the object side, an object side lens sub-unithaving a negative refractive power, and an image side lens sub-unithaving a negative refractive power, each of the object side lenssub-unit and the image side lens sub-unit can include a cemented lens,and a surface of the object side lens sub-unit closest to the objectside and a surface of the image side lens sub-unit closest to the objectside can be both concave surfaces and can be both concave towards theobject side.

In the configuration described above, a negative spherical aberrationoccurring in the first lens unit can be reduced with a positivespherical aberration occurring in the second lens unit. Here, the shapeof a surface of the second lens unit closest to the object side cancontribute to a positive spherical aberration occurring in the secondlens unit. In a case where the second lens unit is constituted by theobject side lens sub-unit and the image side lens sub-unit, the surfaceof the second lens unit closest to the object side can correspond to asurface of the object side lens sub-unit closest to the object side.

In view of this, both the surface of the object side lens sub-unitclosest to the object side and the surface of the image side lenssub-unit closest to the object side can have their concave surfacesfacing the object side. In this manner, a positive spherical aberrationoccurring in the second lens unit can be dispersed in the two surfaces.Thus, it is possible to prevent an excessive increase in the amount of apositive spherical aberration occurring in the second lens unit whilemaintaining a desired magnification.

As described above, a negative spherical aberration can occur in thefirst lens unit. In view of this, a positive spherical aberrationoccurring in the second lens unit can be dispersed so that the positivespherical aberration in an amount necessary for reducing a negativespherical aberration can be generated in the second lens unit.

In addition, since the surface of the object side lens sub-unit closestto the object side and the surface or the image side lens sub-unitclosest to the object side have their concave surfaces facing the objectside, aberrations, especially a spherical aberration and a chromaticaberration, occurring in each lens surface can be reduced, therebyenabling good aberration reduction. Furthermore, influences oneccentricity can be reduced, thereby obtaining good assemblyperformance.

A converter lens device according to a fifth embodiment has a similarconfiguration as the embodiments described above. The fifth embodimentis of a configuration in which the second lens unit can includesequentially from the object side, an object side lens sub-unit having anegative refractive power, and an image side lens subunit having anegative refractive power, a surface of the object side lens sub-unitclosest to the object side can have its concave surface facing theobject side, and the image side lens sub-unit can include a cementedlens composed of three lenses.

As described above, since the image side lens sub unit can include thecemented lens, processability and assembly performance of the image sidelens sub-unit can be enhanced. In addition, since the cemented lens iscomposed of three lenses, aberrations can be reduced. To reduceaberrations, the cemented lens can be composed of three lenses of anegative lens, a positive lens, and a negative lens.

A converter lens device according to a sixth embodiment has a similarconfiguration as the embodiments described above. The sixth embodimentis of a configuration in which the second lens unit can includesequentially from the object side, an object side lens sub-unit having anegative refractive power, and an image side lens sub-unit having anegative refractive power, and the image side lens sub-unit can includea cemented lens composed of three lenses, and can satisfy conditionalexpression (4):−2.0≦(r _(21f) +r _(21r))/(r _(21f) −r _(21r))≦2.0  (4)where

-   -   r_(21f) is a radius of curvature of a surface of the object side        lens sub-unit closest to the object side, and    -   r_(21r) is a radius of curvature of a surface of the object side        lens sub-unit closest, to the image side.

As described above, since the image side lens sub-unit can include thecemented lens composed of the three lenses, processability and assemblyperformance of the image side lens sub-unit can be enhanced, andaberrations can be reduced.

Conditional expression (4) is a conditional expression with respect tothe shape of the object side lens sub-unit. Aberrations can be reducedby avoiding values above the upper limit of conditional expression (4)or values below the lower limit thereof.

A converter lens device according to a seventh embodiment has a similarconfiguration as those described above. The seventh embodiment is of aconfiguration in which the second lens unit can include sequentiallyfrom the object side, an object side lens sub-unit having a negativerefractive power, and an image side lens sub-unit having a negativerefractive power, the object side lens sub-unit can include a cementedlens, and the third lens unit can include a cemented lens.

As described above, since the object side lens sub-unit can include thecemented lens, differences in a spherical aberration and a comaaberration depending on the wavelength can be reduced.

Since the third lens unit can include the cemented lens, occurrence of amagnification chromatic aberration can be suppressed. In a case wherethe cemented lens of the third lens unit is composed of the positivelens and the negative lens, the incident angle of off-axis rays at theinterface can be reduced. Consequently, the magnification chromaticaberration can be reduced. The cemented lens of the third lens unitcomposed of the positive lens and the negative lens can be advantageousfor reducing the magnification chromatic aberration.

A converter lens device according to an eighth embodiment has a similarconfiguration as those embodiments described, above. The eighthembodiment is of a configuration in which the first lens unit caninclude a cemented lens, the second lens unit can include sequentiallyfrom the object side, an object side lens sub-unit having a negativerefractive power, and an image side lens sub-unit having a negativerefractive power, and the image side lens sub-unit can include acemented lens.

Since the first lens unit can include the cemented lens, a chromaticaberration can be reduced.

The cemented lens of the first lens unit may be composed of a negativelens and a positive lens. Then, the incident angle of axial rays at theinterface can be reduced. Consequently, the difference in a sphericalaberration depending on the wavelength can be reduced.

A converter lens device according to a ninth embodiment has a similarconfiguration as those embodiments described above. The ninth embodimentis of a configuration in which the second lens unit can includesequentially from the object side, an object side lens sub-unit having anegative refractive power, and an image side lens sub-unit having anegative refractive power, and the image side lens sub-unit can includea cemented lens, and can satisfy conditional expression (8):−2.4≦f ₃ /f≦−75  (8)where

-   -   f₃ is a focal length of the third lens unit, and    -   f is a focal length of the converter lens.

As described above, since the image side lens sub-unit can include thecemented lens, processability and assembly performance of the image sidelens sub-unit can be enhanced.

An excessive increase in the refractive power of the third lens unit canbe prevented by avoiding values above the upper limit of conditionalexpression (8). In this case, the necessity of increasing the refractivepower of the second lens unit can be avoided and the occurrence ofaberrations can be suppressed.

An excessive increase in the emergence angle of off-axis rays (principalrays) emitted from the third lens unit is reduced by avoiding valuesbelow the lower limit of conditional expression (8). In view of this,the incident angle of rays incident on the image pickup sensor can beset at an angle satisfying incidence characteristics of the image pickupsensor.

A converter lens device according to a tenth embodiment has a similarconfiguration as those embodiments described above. The tenth embodimentis of a configuration in which the first lens unit can include acemented lens, and the second lens unit can include sequentially fromthe object side, an object side lens sub-unit having a negativerefractive power, and an image side lens sub-unit having a negativerefractive power, and can satisfy conditional expression (8′):−2.4≦f ₃ /f≦−1.0  (8′)wherein

-   -   f₃ is a focal length of the third lens unit, and    -   f is a focal length of the converter lens.

As described above, since the first lens unit can include the cementedlens, a chromatic aberration can be reduced. Technical significance ofconditional expression (8′) is similar to that of conditional expression(8).

In addition, the converter lens devices of the first through tenthembodiments (hereinafter collectively referred to as a “converter lensdevice of the present embodiment”) can satisfy conditional expression(1) described above.

In the converter lens device of the present embodiment, the second lensunit can include sequentially from the object side, an object side lenssub-unit having a negative refractive power, and an image side lenssub-unit having a negative refractive power, and conditional expression(2) or (2′) described above can be satisfied.

The converter lens device of the present embodiment can satisfyconditional expression (3)0.3≦f ₂₃ /f≦0.9  (3)wherein

-   -   f₂₃ is a composite focal length of the second lens unit and the        third lens unit, and    -   f is a focal length of the converter lens.

Since the composite focal length of the second lens unit and the thirdlens unit has a negative value, a composite refractive power of thesecond lens unit and the third lens unit is a negative refractive power.In this case, the principal point of the converter lens can approach theobject side. Thus, the refractive power of the converter lens can bemaintained. Consequently, good aberration reduction can be achieved witha small number of lenses.

An increase in the total length of the converter lens can be preventedby avoiding values above the upper limit of conditional expression (3).An increase in the refractive power of the converter lens can beprevented by avoiding values below the lower limit of conditionalexpression (3). Consequently, degradation of a spherical aberration andan increase in the number of lenses can be suppressed.

In addition, in the converter lens device of the present embodiment, thesecond lens unit can include an object side lens sub-unit having anegative refractive power, and the converter lens device can satisfyconditional expression (4):−2.0≦(r _(21f) +r _(21r))/(r _(21f) −r _(21r))≦2.0  (4)where

-   -   r_(21f) is a radius of curvature of a surface of the object side        lens sub-unit closest to the object side, and    -   r_(21r) is a radius of curvature of a surface of the object side        lens sub-unit closest, to the image side.

In the converter lens device of the present embodiment, the second lensunit can include an image side lens sub-unit having a negativerefractive power, and the converter lens device can satisfy conditionalexpression (5):−2.0≦(r _(22f) +r _(22r))/(r _(22f) −r _(22r))≦0  (5)wherein

-   -   r_(22f) is a radius of curvature of a surface of the image side        lens sub-unit closest to the object side, and    -   r_(22r) is a radius of curvature of a surface of the image side        lens sub-unit closest to the image side.

Conditional expression (5) is a conditional expression with respect tothe shape of the image side lens sub-unit. Good aberration reduction canbe obtained by avoiding values above the upper limit of conditionalexpression (5) or values below the lower limit thereof.

By avoiding values above the upper limit of condltional expression (5),occurrence of ghosts in the surface of the image side lens sub-unitclosest to the image side can be suppressed. Thus, values above theupper limit of conditional expression (5) can be avoided.

In the converter lens device of the present embodiment, the second lensunit can include an image side lens sub-unit having a negativerefractive power, and the converter lens device can satisfy conditionalexpression (6):1.75≦nd _(22N)≦2.00  (6)where

-   -   nd_(22N) is an average value of refractive indexes on a d line        in a negative lens included in the image side lens sub-unit.

Conditional expression (6) is a conditional expression with respect torefractive indexes of a negative lens included in the image side lenssub-unit. In the image side lens sub-unit, the height of axial rays isrelatively low. In a configuration in which the negative lens includedin the image side lens sub-unit has a large refractive power,degradation of curvature of field can be prevented by appropriatelysetting the values of refractive indexes of the negative lens.

The degradation of curvature of field can be prevented by avoidingvalues below the lower limit of conditional expression (6). Thus, valuesbelow the lower increase in cost of a glass material can be prevented byavoiding values above the upper limit of conditional expression (6).Thus, values above the upper limit of conditional expression (6) can beavoided.

In the converter lens device of the present embodiment, the second lensunit can include an image side lens sub-unit having a negativerefractive power, and the converter lens device can satisfy conditionalexpression (7):25≦νd _(22N)≦50  (7)where

-   -   νd_(22N) is an average value of Abbe numbers with respect to a d        line of a negative lens included in the image side lens        sub-unit.

Conditional expression (7) is a conditional expression with respect toAbbe numbers of the negative lens included in the image side lenssub-unit. Since each negative lens included in the image side lenssub-unit has a large refractive power, degradation of a chromaticaberration can occur unless the values of Abbe numbers of the negativelens are not appropriately set.

Degradation of a chromatic aberration can be prevented by avoidingvalues below the lower limit of conditional expression (7). Thus, it ispossible to avoid values below the lower limit of conditional expression(7). An excessive decrease in the refractive index can be Prevented byavoiding values above the upper limit of conditional expression (7).Thus, a generally available glass material can be used. Consequently,both the curvature of field and the chromatic aberration can be reduced.

In the converter lens device of the present embodiment, the second lensunit can include sequentially from the object side, an object side lenssub-unit having a negative refractive power and an image side lenssub-unit.

The second lens unit constituted by the two lens sub-units can obtaingood aberration reduction, enhance assembly performance of the opticalsystem, and suppress occurrence of ghosts.

In the converter lens device of the present embodiment, the second lensunit can include sequentially from the object side, an object side lenssub-unit and an image side lens sub-unit having a negative refractivepower.

The second lens unit constituted by the two lens sub-units can obtaingood aberration reduction, enhance assembly performance of the opticalsystem, and suppress occurrence of ghosts.

In the converter lens device of the present embodiment, the second lensunit can include an object side lens sub-unit having a negativerefractive power, and a surface of the object side lens sub-unit closestto the object side can have its concave surface facing the object side.

In this manner, occurrence of a spherical aberration in the first lensunit and the second lens unit can be suppressed.

In the converter lens device of the present embodiment, the second lensunit can include an image side lens sub-unit having a negativerefractive power, and a surface of the image side lens sub-unit closestto the object side can have its concave surface facing the object side.

In this manner, occurrence of a spherical aberration in the first lensunit and the second lens unit can be suppressed.

In the converter lens device of the present embodiment, the second lensunit can include an object side lens sub-unit having a negativerefractive power, and the object side lens sub-unit can include acemented lens.

In this manner, differences in a spherical aberration and a comaaberration depending on the wavelength can be reduced.

In the converter lens device of the present embodiment, the second lensunit can include an image side lens sub-unit having a negativerefractive power, and the image side lens sub-unit can include acemented lens.

In this manner, processability and assembly performance of the imageside lens sub-unit can be enhanced.

In the converter lens device of the present embodiment, the second lensunit can include an image side lens sub-unit having a negativerefractive power, and the image side lens sub-unit can include acemented lens composed of three lenses.

In this manner, processability and assembly performance of the imageside lens sub-unit can be enhanced, and aberrations can be reduced.

In the converter lens device of the present embodiment, the first lensunit can include a cemented lens.

In this manner, a chromatic aberration can be reduced.

In the converter lens device of the present embodiment, the third lensunit can have a positive refractive power.

In the configuration in which the converter lens is constituted by thefirst lens unit having the positive refractive power, the second lensunit having the negative refractive power, and the third lens unithaving the positive refractive power, a spherical aberration and a comaaberration can be reduced with the first lens unit and the second lensunit, and distortion can be reduced with the second lens unit and thethird lens unit. The positive refractive power of the third lens unitcan prevent an excessive increase in the emergence angle of off-axisrays (principal rays) emitted from the converter lens. Thus, theincident angle of rays incident on the image pickup sensor disposedclose to the image surface can be reduced.

The converter lens device of the present embodiment can satisfyconditional expression (8):−2.4≦f ₃ /f≦−75  (8)where

-   -   f₃ is a focal length of the third lens unit, and    -   f is a focal length of the converter lens.

In the converter lens device of the present embodiment, the third lensunit can include a cemented lens.

In this manner, occurrence of a magnification chromatic aberration canbe suppressed.

In the converter lens device of the present embodiment, the first lensunit can include a negative meniscus lens whose convex surface faces theobject side and a biconvex positive lens.

In this manner, a chromatic aberration that can occur in the first lensunit can be reduced. The use of the biconvex positive lens can obtain anappropriate incident angle of rays incident on each lens surface.

In the converter lens device of the present embodiment, the third lensunit can include a biconvex positive lens and a negative meniscus lenswhose convex surface faces the image side.

In this manner, the incident angle of off-axis rays can be reduced, andthus, occurrence of aberrations can be suppressed.

The converter lens device of the present embodiment can satisfyconditional expression (9):−5.0≦f ₁ /f ₂₃≦1.0  (9)where

-   -   f₁ is a focal length of the first lens unit, and    -   f₂₃ is a composite focal length of the second lens unit and the        third lens unit.

A telecentric optical system obtains an advantage in which principalrays emitted from the optical system are parallel to the optical axis.By avoiding values above the upper limit of conditional expression (9),advantages in the telecentric optical system can be sufficientlyobtained with the converter lens of the present embodiment, and anincrease in the total length of the optical system can be suppressed.

An increase in occurrence of aberrations in the second lens unit and thethird lens unit can be suppressed avoiding values below the lower limitof conditional expression (9).

The converter lens device of the present embodiment can satisfyconditional expression (10):−3.0≦f ₁ /f≦−1.0  (10)wherein

-   -   f₁ is a focal length of the first lens unit, and    -   f is a focal length of the converter lens.

An increase in occurrence of aberrations in the first lens unit can besuppressed by avoiding values above the upper limit of conditionalexpression (10). An increase in the outer diameter of the converter lenscan be suppressed by avoiding values below the lower limit ofconditional expression (10).

The converter lens device of the present embodiment can satisfyconditional expression (11):0.2≦f ₂ /f≦0.6  (11)wherein

-   -   f₂ is a focal length or the second lens unit, and    -   f is a focal length of the converter lens.

An increase in the total length of the optical system can be suppressedby avoiding values above the upper limit of conditional expression (11).An increase in occurrence of aberrations in the second lens unit can besuppressed by avoiding values below the lower limit of conditionalexpression (11).

In the converter lens device of the present embodiment, the negativerefractive power of the image side lens sub-unit can be larger than thenegative refractive power of the object side lens sub-unit.

In this manner, the principal point of the converter lens can bedisposed close to the object side. Consequently, the refractive power ofthe converter lens can be reduced, and thus, aberrations can be reduced.The increase in the negative refractive power of the image side lenssub-unit can be also advantageous in view of aberration reduction.

A photographing system according to the present embodiment can include:a master lens device; a camera body including an image pickup sensor;and a converter lens device attachable between the master lens deviceand the camera body. In the photographing system, an optical systemconstituted by the master lens device and the converter lens deviceforms an image of an object, the image pickup sensor is disposed at animage position of the object and converts an image of the object into anelectric signal, and the converter lens device can include one of theabove-described converter lenses.

In the photographing system according to the present embodiment, a newcamera system having a relatively short flange focal distance can alsoacquire a high-quality image with a sufficient magnification.

A plurality of the abovementioned arrangements can be simultaneouslysatisfied interactively. In this manner, a high-quality optical systemcan be acquired. Combinations of some aspects of examples arechangeable. Regarding each conditional expression, restricting one ofthe lower limit value and the upper limit value, or both, can be done.

For conditional expression (1), the lower limit value can be 0.22, 0.30,0.34 or 0.45. Moreover, for conditional expression (1), the upper limitvalue can be 0.82, 0.78, 0.75 or 0.73.

For conditional expression (2), the lower limit value can be 1.950.Moreover, for conditional expression (2), the upper limit value can be14.63, 11.26, 10.0, or 7.89.

For conditional expression (2′), the lower limit value can be 1.05, 1.5,1.7 or 1.95. Moreover, for conditional expression (2′), the upper limitvalue can be 7.89, 7.0, 6.0, or 5.0.

For conditional expression (3), the lower limit value can be 0.37, 0.43,or 0.50. Moreover, for conditional expression (3), the upper limit valuecan be 0.84, 0.79, or 0.73.

For conditional expression (4), the lower limit value can be −1.63,−1.26, or −0.89. Moreover, for condltional expression (4), the upperlimit value can be 1.61, 1.23, or 0.84.

For conditional expression (5), the lower limit value can be −1.80,−1.59, or −1.39. Moreover, for conditional expression (5), the upperlimit value can be −0.081, −0.16, or −0.24.

For conditional expression (6), the lower limit value can be 1.77, 1.80,or 1.82. Moreover, for conditional expression (6), the upper limit valuecan be 1.97, 1.94, or 1.91.

For conditional expression (7), the lower limit value can be 26.5, 27.9,or 29.4. Moreover, for conditional expression (7), the upper limit valuecan be 48.4, 46.8, or 45.3.

For conditional expression (8), the lower limit value can be −2.3, −2.2,or −2.0. Moreover, for conditional expression (8), the upper limit valuecan be −0.84, −0.93, or −1.0.

For conditional expression (8′), the lower limit value can be −2.3,−2.2, or −2.0. Moreover, for conditional expression (8′), the upperlimit value can be −1.0.

For conditional expression (9), the lower limit value can be −4.6, −4.2,or −3.8. Moreover, for conditional expression (9), the upper limit valuecan be −1.4, −1.8, or −2.2.

For conditional expression (10), the lower limit value can be −2.8,−2.6, or −2.5. Moreover, for conditional expression (10), the upperlimit value can be −1.1, −1.3, or −1.4.

For conditional expression (11), the lower limit value can be 0.23,0.27, or 0.30. Moreover, for conditional expression (11), the upperlimit value can be 0.57, 0.55, of 0.52.

Examples of converter lens according to certain aspects of the presentinvention will be described below in detail by referring to theaccompanying diagrams. However, the present invention is not restrictedto the examples described below.

Next, converter lens according to examples from an example 1 to anexample 6 will be described below. FIG. 1 to FIG. 6 are lenscross-sectional views. Moreover, a first lens unit is denoted by G1, asecond lens unit is denoted by G2, a third lens unit is denoted by G3,and an image plane (image pickup surface) is denoted by I.

A flat and parallel plate which forms a low-pass filter or a cover glassof an electronic image pickup sensor may be disposed between the thirdlens unit and the image plane I. A wavelength region restricting coatingwhich restricts infrared light may be applied to a surface or the flatand parallel plate. Moreover, a multilayer film for restrictingwavelength region may be applied to a surface of the cover glass. Thecover glass may be imparted an effect of a low-pass filter. In eachexample, a cover glass CG can be disposed.

In each examples, an image plane I denotes an image plane in combinationof a master lens and a converter lens. An image pickup sensor can bedisposed at image plane T.

FIG. 1 is a lens cross sectional view of a converter lens according toexample 1. The converter lens can include sequentially from an objectside, a first lens unit G1 having a positive refractive power, a secondlens unit G2 having a negative refractive power, and a third lens unitG3 having a positive refractive power.

The first lens unit G1 can include a negative meniscus lens L1 having aconvex surface facing the object side, a biconvex positive lens L2.Here, the negative meniscus lens L1 and the biconvex positive lens L2are cemented.

The second lens unit G2 can include a positive meniscus lens L3 having aconvex surface facing the image side, a biconcave negative lens L4, abiconcave negative lens L5, a biconvex positive lens L6, and a biconcavenegative lens L7. Here, the positive meniscus lens L3 and the biconcavenegative lens L4 are cemented. The biconcave negative lens L5, thebiconvex positive lens and the biconcave negative lens L7 are cemented.

The second lens unit G2 can include an object side lens sub-unit havinga negative refractive power and an image side lens sub-unit having anegative refractive power. The object side lens sub-unit can include thepositive meniscus lens L3 and the biconcave negative lens L4. The imageside lens sub-unit can include the biconcave negative lens L5, thebiconvex positive lens L6, and the biconcave negative lens L7.

The third lens unit G3 can include a biconvex positive lens L8, anegative meniscus lens L9 having a convex surface facing the image side.Here, the biconvex positive lens L8 and the negative meniscus lens L9are cemented.

FIG. 2 is a lens cross sectional view of a converter lens according toexample 2 The converter lens can include sequentially from an objectside, a first lens unit G1 having a positive refractive power, a secondlens unit G2 having a negative refractive power, and a third lens unitG3 having a positive refractive power.

The first lens unit G1 can include a negative meniscus lens L1 having aconvex surface facing the object side, a biconvex positive lens L2.Here, the negative meniscus lens L1 and the biconvex positive lens L2are cemented.

The second lens unit G2 can include a positive meniscus lens L3 having aconvex surface facing the image side, a biconcave negative lens L4, abiconcave negative lens L5, a biconvex positive lens L6, and a negativemeniscus lens L7 having a convex surface facing the image side. Here,the positive meniscus lens L3 and the biconcave negative lens L4 arecemented. The biconcave negative lens L5, the biconvex positive lens L6and the negative meniscus lens L7 are cemented.

The second lens unit G2 can include an object side lens sub-unit havinga negative refractive power and an image side lens sub-unit having anegative refractive power. The object side lens sub-unit can include thepositive meniscus lens L3 and the biconcave negative lens L4. The imageside lens sub-unit can include the biconcave negative lens L5, thebiconvex positive lens L6, and the negative meniscus lens L7.

The third lens unit G3 can include a biconvex positive lens L3, anegative meniscus lens L9 having a convex surface facing the image side.Here, the biconvex positive lens L3 and the negative meniscus lens L9are cemented.

FIG. 3 is a lens cross sectional view of a converter lens according toexample 3. The converter lens can include sequentially from an objectside, a first lens unit G1 having a positive refractive power, a secondlens unit G2 having a negative refractive power, and a third lens unitG3 having a positive refractive power.

The first lens unit G1 can include a negative meniscus lens L1 having aconvex surface facing the object side, a biconvex positive lens L2.Here, the negative meniscus lens L1 and the biconvex positive lens L2are cemented.

The second lens unit G2 can include a positive meniscus lens L3 having aconvex surface facing the image side, a biconcave negative lens L4, abiconcave negative lens L5, a biconvex positive lens L6, and a negativemeniscus lens L7 having a convex surface facing the image side. Here,the positive meniscus lens L3 and the biconcave negative lens L4 arecemented. The biconcave negative lens L5, the biconvex positive lens L6and the negative meniscus lens L7 are cemented.

The second lens unit G2 can include an object side lens sub-unit havinga negative refractive power and an image side lens sub-unit having anegative refractive power. The object side lens sub-unit can include thepositive meniscus lens L3 and the biconcave negative lens L4. The imageside lens sub-unit can include the biconcave negative lens L5, thebiconvex positive lens L6, and the negative meniscus lens L7.

The third lens unit G3 can include a biconvex positive lens L8, anegative meniscus lens L9 having a convex surface facing the image side.Here, the biconvex positive lens L8 and the negative meniscus lens L9are cemented.

FIG. 4 is a lens cross sectional view of a converter lens according toexample 4. The converter lens can include sequentially from an objectside, a first lens unit G1 having a positive refractive power, a secondlens unit G2 having a negative refractive power, and a third lens unitG3 having a positive refractive power.

The first lens unit G1 can include a negative meniscus lens L1 having aconvex surface facing the object side, a biconvex positive lens L2.Here, the negative meniscus lens L1 and the biconvex positive lens L2are cemented.

The second lens unit G2 can include a biconcave negative lens L3, apositive meniscus lens L4 having a convex surface facing the objectside, a biconcave negative lens L5, a biconvex positive lens L6, and anegative meniscus lens L7 having a convex surface facing the image side.Here, the biconcave negative lens L3 and the positive meniscus lens L4are cemented. The biconcave negative lens L5, the biconvex positive lensL6 and the negative meniscus lens L7 are cemented.

The second lens unit G2 can include an object side lens sub-unit havinga negative refractive power and an image side lens sub-unit having anegative refractive power. The object side lens sub-unit can include thebiconcave negative lens L3 and the positive meniscus lens L4. The imageside lens sub-unit can include the biconcave negative lens L5, thebiconvex positive lens L6, and the negative meniscus lens L7.

The third lens unit G3 can include a biconvex positive lens L8, anegative meniscus lens L9 having a convex surface facing the image side.Here, the biconvex positive lens L8 and the negative meniscus lens L9are cemented.

FIG. 5 is a lens cross sectional view of a converter lens according toexample 5. The converter lens can include sequentially from an objectside, a first lens unit G1 having a positive refractive power, a secondlens unit G2 having a negative refractive power, and a third lens unitG3 having a positive refractive power.

The first lens unit G1 can include a negative meniscus lens L1 having aconvex surface facing the object side, a biconvex positive lens L2.Here, the negative meniscus lens L1 and the biconvex positive lens L2are cemented.

The second lens unit G2 can include a biconcave negative lens L3, abiconvex positive lens L4, and a biconcave negative lens L5. Here, thebiconcave negative lens L3 and the biconvex positive lens 14 arecemented.

The second lens unit G2 can include an image side lens sub-unit having anegative refractive power. The image side lens sub-unit can include thebiconcave negative lens L3, the biconvex positive lens L4, and thebiconcave negative lens L5.

The third lens unit G3 can include a biconvex positive lens L6, and abiconcave negative lens L7. Here, the biconvex positive lens L6 and thebiconcave negative lens L7 are cemented.

FIG. 6 is a lens cross sectional view of a converter lens according toexample 6. The converter lens can include sequentially from an objectside, a first lens unit G1 having a positive refractive power, a secondlens unit G2 having a negative refractive power, and a third lens unitG3 having a positive refractive power.

The first lens unit G1 can include a negative meniscus lens L1 having aconvex surface facing the object side, a biconvex positive lens L2.Here, the negative meniscus lens L1 and the biconvex positive lens L2are cemented.

The second lens unit G2 can include a biconcave negative lens L3, abiconcave negative lens L4, a biconvex positive lens L5, and a biconcavenegative lens L6. Here, the biconcave negative lens L4, the biconvexpositive lens L5, and the biconcave negative lens L6 are cemented.

The second lens unit G2 can include an object side lens sub-unit havinga negative refractive power and an image side lens sub-unit having anegative refractive power. The object side lens sub-unit can include thebiconcave negative lens L3. The image side lens sub-unit can include thebiconcave negative lens L4, the biconvex positive lens L5, and thebiconcave negative lens L6.

The third lens unit G3 can include a biconvex positive lens L7, and anegative meniscus lens L8 having a convex surface facing the image side.Here, the biconvex positive lens L7 and the negative meniscus lens L8are cemented.

Next, an example of a master lens is described. FIG. 13 is a lens crosssectional view or the master lens.

As described in the FIG. 13, the master lens can include sequentiallyfrom the object side, a cemented lens including a negative meniscus lenshaving a convex surface facing the object side and a biconvex positivelens, a positive meniscus lens having a convex surface facing the objectside, a positive meniscus lens having convex surface facing the imageside, a cemented lens including a biconcave negative lens and a positivemeniscus lens having a convex surface facing the object side, abiconcave negative lens, an aperture stop, a biconvex positive lens, acemented lens including a negative meniscus lens having a convex surfacefacing the object side and a biconvex positive lens, a biconvex positivelens, a cemented lens including a biconvex positive lens and a biconcavenegative lens, a biconcave negative lens, a cemented lens including abiconvex positive lens and a plano-concave negative lens.

FIG. 14 is a lens cross sectional view of incorporation the converterlens with the master lens. In FIG. 14, the converter lens of example 1is used. In FIG. 14, the lenses from r1 through r27 are the master lensand the lenses from r28 through r40 are the converter lens.

Set out below are a variety of numeral data (surface data, etc.) aboutthe examples. The surface data includes the radius of curvature r andsurface separation d of each lens surface (optical surface) for eachsurface number, the d-line (587.6 nm) refractive index nd of each lens(optical medium), and the d-line Abbe constant νd of each lens (opticalmedium). Various data include focal lengths f, F-numbers (FNO), anglesof view 2ω°, back focuses BF (in air), total lengths (in air),magnification 13, and image heights IH. Note here that BF is a distancefrom the final lens surface to the image plane as calculated on an airbasis. The total length is defined as the sum of the back focus and adistance from a forefront lens surface to a last lens surface. Thesevarious data are the data in the case of incorporation the converterlens with the master lens.

Example 1

A converter lens of embodiment 1 is discussed in this example.

Unit mm Surface data Surface no. r d nd νd 1 65.1918 1.0000 1.8830040.76 2 17.2989 6.3400 1.67270 32.10 3 −41.2599 0.7400 4 −112.35603.4900 1.59270 35.31 5 −28.4752 1.0000 1.88300 40.76 6 130.5475 2.0000 7−50.9966 1.0000 1.88300 40.76 8 29.0155 6.4100 1.59270 35.31 9 −19.76071.0000 1.88300 40.76 10 99.9691 0.2000 11 23.7389 6.7300 1.59270 35.3112 −23.7389 1.3900 1.92286 18.90 13 −67.9266 12.3234 14 ∞ 4.0000 1.5163364.14 15 ∞ 0.8000 Image plane Distance between the master lens and theconverter lens: 3.2632 Various data (infinite) f 249.93 FNO. 4.95 2ω5.03° IH 10.82 B 1.70 BF (in air) 15.76 Total length (in air) 200.72

Example 2

Unit mm Surface data Surface no. r d nd νd 1 84.7892 1.0000 1.8348142.73 2 15.8489 6.6200 1.59270 35.31 3 −32.3018 0.8000 4 −71.3421 3.13001.59270 35.31 5 −35.0798 1.0000 1.72916 54.68 6 160.6126 2.0800 7−40.0219 1.0000 1.81600 46.62 8 23.6378 6.5200 1.59270 35.31 9 −17.29411.0000 1.88300 40.76 10 −475.2016 0.2000 11 24.1647 6.1000 1.59270 35.3112 −24.1647 1.3000 1.92286 20.88 13 −109.0509 21.7191 14 ∞ 4.00001.51633 64.14 15 ∞ 0.8000 Image plane Distance between the master lensand the converter lens: 2.2632 Various data (infinite) f 294.03 FNO.5.76 2ω 4.27° IH 10.82 β 2.00 BF (in air) 25.16 Total length (in air)208.57

Example 3

Unit mm Surface data Surface no. r d nd νd 1 87.2894 1.0000 1.8348142.73 2 17.1399 6.4100 1.59270 35.31 3 −35.4760 0.7600 4 −73.2984 3.18001.59270 35.31 5 −33.9580 1.0000 1.59282 68.63 6 204.4691 1.9500 7−46.5721 1.0000 1.88300 40.76 8 21.4391 6.6800 1.59270 35.31 9 −18.63681.0000 1.88300 40.76 10 −1885.0868 0.2000 11 23.4145 6.2700 1.5927035.31 12 −23.4145 1.3000 1.92119 23.96 13 −158.1720 22.5769 14 ∞ 4.00001.51633 64.14 15 ∞ 0.8000 Image plane Distance between the master lensand the converter lens: 1.2632 Various data (infinite) f 293.86 FNO.5.76 2ω 4.26° IH 10.82 β 2.00 BF (in air) 26.01 Total length (in air)208.43

Example 4

Unit mm Surface data Surface no. r d nd νd 1 92.3720 1.0000 1.8348142.71 2 15.8334 6.7500 1.59270 35.31 3 −30.7777 0.7100 4 −58.6451 1.00001.74100 52.64 5 14.8334 4.9300 1.78472 25.68 6 189.0857 2.1600 7−34.7689 1.0000 1.92286 18.90 8 20.3359 6.1200 1.67270 32.10 9 −19.04961.0000 1.83481 42.71 10 −3918.8699 0.2000 11 24.1623 5.8900 1.5927035.31 12 −24.1623 1.3000 1.83481 42.71 13 −172.4865 23.4353 14 ∞ 4.00001.51633 64.14 15 ∞ 0.8000 Image plane Distance between the master lensand the converter lens: 1.2632 Various data (infinite) f 294.06 FNO.5.76 2ω 4.27° IH 10.82 β 2.00 BF (in air) 26.87 Total length (in air)210.59

Example 5

Unit mm Surface data Surface no. r d nd νd 1 110.5546 1.0000 1.8348142.73 2 17.1310 6.5900 1.57501 41.50 3 −29.7379 2.4600 4 −34.3494 1.00001.88300 40.76 5 15.6142 7.4300 1.76182 26.52 6 −20.6672 1.0000 1.8830040.76 7 72.5300 0.2000 8 21.8102 5.5900 1.59270 35.31 9 −28.6544 1.30001.92286 18.90 10 325.8668 26.9757 11 ∞ 4.0000 1.51633 64.14 12 ∞ 0.8000Image plane Distance between the master lens and the converter lens:1.2632 Various data (infinite) f 293.95 FNO. 5.76 2ω 4.22° IH 10.82 β2.00 BF (in air) 30.41 Total length (in air) 208.65

Example 6

Unit mm Surface data Surface no. r d nd νd 1 40.8655 1.0000 1.8348142.73 2 14.0063 6.6400 1.59270 35.31 3 −37.6568 0.6600 4 −148.07411.0000 1.83481 42.73 5 55.0766 2.3300 6 −39.9517 1.0000 1.88300 40.76 716.8494 7.6500 1.67270 32.10 8 −16.8494 1.0000 1.88300 40.76 9 307.70750.2000 10 23.5892 6.7900 1.59270 35.31 11 −23.5892 1.3000 1.92286 20.8812 −96.1183 22.0470 13 ∞ 4.0000 1.51633 64.14 14 ∞ 0.8000 Image planeDistance between the master lens and the converter lens: 2.2632 Variousdata (infinite) f 293.99 FNO. 5.76 2ω 4.25° IH 10.82 β 2.00 BF (in air)25.49 Total length (in air) 207.72Example of Master Lens

Unit mm Surface data Surface no. r d nd νd  1 137.0268 2.6000 1.7847026.29  2 86.6508 7.7600 1.49700 81.61  3 −321.6069 0.1500  4 96.81545.2600 1.43875 94.93  5 624.2467 53.8789  6 −227.2066 3.3700 1.8081022.76  7 −59.4074 1.6000 1.48749 70.23  8 30.8341 2.7500 1.80000 29.84 9 39.2048 4.9900 10 −49.6375 1.5000 1.83481 42.73 11 458.1191 1.912212(Stop) ∞ 1.8000 13* 39.4392 5.7600 1.49700 81.61 14* −87.6954 7.980015 70.3121 1.5000 1.84666 23.78 16 32.8253 6.5800 1.59282 68.63 17−51.5148 0.1500 18 129.4168 3.1000 1.49700 81.61 19 −94.0670 3.8905 20789.7458 2.0000 1.92286 18.90 21 −86.5458 1.0000 1.74320 49.29 22*21.6608 16.1946 23 −356.0768 1.0000 1.62004 36.26 24 28.8000 2.7919 25*31.6086 9.5800 1.80610 40.88 26 −24.0000 1.3000 1.64769 33.79 27 ∞26.0632 28 ∞ 4.0000 1.51633 64.14 29 ∞ 0.8000 Image plane Asphericalsurface data 13th surface k = 0 A4 = −3.1251E−06, A6 = −3.8756E−10, A8 =5.5927E−11, A10 = −1.4099E−13 14th surface k = 0 A4 = 1.0047E−05, A6 =−3.0390E−10, A8 = 5.4533E−11, A10 = −1.3296E−13 22th surface k = −0.0326A4 = −2.5854E−06, A6 = 2.4119E−09, A8 = −7.1028E−11, A10 = 1.4991E−1325th surface k = −0.7171 A4 = 7.9298E−07, A6 = −2.8322E−09, A8 =2.5344E−12, A10 = 0.0000E+00 Various data (infinite) f 147.00 FNO. 2.882ω 8.30° IH 10.82 BF (in air) 29.50 Total length (in air) 179.90

Aberration diagrams according to the examples from the example 1 to theexample 6 are shown in diagrams from FIG. 7A to FIG. 12D. Theseaberration diagrams are the aberration diagrams in combination of masterlens and a converter lens. In these aberration diagrams, FIG. 7A, FIG.8, FIG. 9A, FIG. 10A, FIG. 11A, and FIG. 12A show a spherical aberration(SA), FIG. 7B, FIG. 8B, FIG. 9B, FIG. 10B, FIG. 11B and FIG. 12B show anastigmatism (AS), FIG. 7C, FIG. 8C, FIG. 9C, FIG. 10C, FIG. 11C and FIG.12C show a distortion (DT), and FIG. 7D, FIG. 8D, FIG. 9D, FIG. 10D,FIG. 11D and FIG. 12D show a chromatic aberration of magnification (CC).Moreover, in each diagram, ‘FIY’ denotes the maximum image height.

Next, values of conditional expressions (1) to (11) in each example aredescribed as below. Moreover, ‘-’ (hyphen) indicates that there is nocorresponding arrangement or conditional expression is not satisfied.

Conditional expressions Example 1 Example 2 Example 3 (1) |f|/(B * D)0.684 0.584 0.572 (2), (2′) f21/f22 2.399 2.769 4.520 (3) f23/f 0.5640.657 0.666 (4) (r21f + r21r)/(r21f − r21r) −0.075 −0.385 −0.472 (5)(r22f + r22r)/(r22f − r22r) −0.324 −1.184 −1.051 (6) nd22N 1.883 1.8501.883 (7) νd22N 40.760 43.690 40.760 (8), (8′) f3/f −1.119 −1.410 −1.590(9) f1/f23 −2.772 −3.185 −3.430 (10) f1/f −1.564 −2.091 −2.286 (11) f2/f0.333 0.411 0.444 Conditional expressions Example 4 Example 5 Example 6(1) |f|/(B * D) 0.593 0.690 0.605 (2), (2′) f21/f22 3.482 — 2.532 (3)f23/f 0.644 0.671 0.562 (4) (r21f + r21r)/(r21f − r21r) −0.527 — 0.458(5) (r22f + r22r)/(r22f − r22r) −1.018 −0.357 −0.770 (6) nd22N 1.8791.883 1.883 (7) νd22N 30.805 40.760 40.760 (8), (8′) f3/f −1.330 −1.918−1.323 (9) f1/f23 −3.026 −3.300 −2.658 (10) f1/f −1.949 −2.216 −1.495(11) f2/f 0.397 0.499 0.357

FIG. 15 is a schematic cross-sectional view of an image pickup system inwhich, the converter lens device according to the present example andthe master lens device have been combined as used in a taking lens.

An image pickup system is a camera system which does not have aquick-return mirror, for example a single-lens mirrorless camera. Thesingle-lens mirrorless camera is formed by a camera body 1, a converterlens device TC, and a master lens device MSL. The flange focal distanceof the single-lens mirrorless camera can be shorter than that or asingle-lens reflex camera.

The camera body 1 can include a mount 2, a filter F, an imaging pickupsensor disposed at imaging plane I, a control circuit 12, and anelectric contact 13 a. The control circuit 12 can control the camerabody 1, the master lens device MSL, and the converter lens device TC.

The converter lens device TC can include a converter lens, a first mountM1, a second mount M2, a holder 4 holding the converter lens, anelectric contact 13 b, 16 a, and a control circuit 15. The controlcircuit 15 can transmit control information from the control circuit 12to the control circuit 18.

The master lens device MSL can include a master lens, a mount 3, aholder 5 holding the master lens, an electric contact 16 b, a controlcircuit 17, and a control circuit 18. The control circuit 17 can be acircuit for controlling an aperture stop S. The control circuit 18 cantransmit control information of an aperture stop S to the controlcircuit 17 and controls focusing.

A screw type mount or a bayonet type mount may be used as the mount 2,3, M1, M2. In FIG. 15, the bayonet type mount is used as the mount 2, 3,M1, M2.

The converter lens device TC can be attached to the master lens deviceMSL via the mount 3 and the first mount M1. The converter lens device TCcan be attached to the camera body 1 via the mount and the mount M2. Inthis way, the master lens device MSL and the converter lens device TCcan be attached to the camera body 1. Therefore, the master lens, theconverter lens, and the image pickup device can be aligned in theoptical axis 8.

Electric contacts can be set on each mount. Therefore the controlcircuit 12, 15, 17, and 13 can be connected electrically by connectingthe camera body 1, the master lens device MSL, and the converter lensdevice TC. In this way, an adjustment of the aperture stop and theadjustment of focusing can be performed by using the control circuit 12,15, 17, and 18.

The converter lens of the converter lens device TC is a teleconverterlens. The abovementioned converter lenses in example 1 to 6 can be usedas the teleconverter lens. Therefore, in the photographing systemaccording to the present embodiment, a camera system having a relativelyshort flange focal distance can also acquire a high-quality image with asufficient magnification.

The present invention can be useful for a converter lens that can reduceaberrations and has a sufficient magnification in spite of its shortflange focal distance. And it can be also useful for a photographingsystem that has a sufficient magnification and can acquire high qualityimages.

What is claimed is:
 1. A converter lens device comprising: a first mountto which a master lens device is attached; a second mount to which acamera body is attached; and a converter lens having a negativerefractive power, wherein, a focal length, in which the converter lensand the master lens are combined, is longer than a focal length of themaster lens, the converter lens comprises sequentially from an objectside, a first lens unit of a positive refractive power, a second lensunit of a negative refractive power, and a third lens unit, and whereinthe converter lens device satisfies conditional expression (1):0.1≦|f|/(β×D)≦0.87  (1) where an object side of the converter lensdevice is a side closer to the first mount, an image side of theconverter lens device is a side closer to the second mount, f is a focallength of the converter lens, β is a magnification of the converterlens, and D is a thickness of the converter lens on an optical axis,wherein the second lens unit comprises sequentially from the objectside, an object side lens sub-unit having a negative refractive power,and an image side lens sub-unit.
 2. The converter lens device accordingto claim 1, wherein the converter lens satisfies conditional expression(3):0.3≦f ₂₃ /f≦0.9  (3) wherein f₂₃ is a composite focal length of thesecond lens unit and the third lens unit, and f is a focal length of theconverter lens.
 3. The converter lens device according to claim 1,wherein and the converter lens device satisfies conditional expression(4):−2.0≦(r _(21f) +r _(21r))/(r _(21f) −r _(21r))≦2.0  (4) wherein r_(21f)is a radius of curvature of a surface of the object side lens sub-unitcloser to the object side, and r_(21r) is a radius of curvature of asurface of the object side lens sub-unit closer to the image side. 4.The converter lens device according to claim 1, wherein the second lensunit comprises an image side lens sub-unit having a negative refractivepower, and the converter lens device satisfies conditional expression(5):−2.0≦(r _(22f) +r _(22r))/(r _(22f) −r _(22r))≦0  (5) wherein r_(22f) isa radius of curvature of a surface of the image side lens sub-unitcloser to the object side, and r_(22r) is a radius of curvature of asurface of the image side lens sub-unit closer to the image side.
 5. Theconverter lens device according to claim 4, wherein the second lens unitcomprises an image side lens sub-unit having a negative refractivepower, and the converter lens device satisfies conditional expression(7):25≦νd _(22N)≦50  (7) wherein νd_(22N) is an average value of Abbenumbers with respect to a d line of a negative lens included in theimage side lens sub-unit.
 6. The converter lens device according toclaim 1, wherein the second lens unit comprises an image side lenssub-unit having a negative refractive power, and the converter lensdevice satisfies conditional expression (6):1.75≦nd _(22N)≦2.00  (6) wherein nd_(22N) is an average value ofrefractive indexes on a d line in a negative lens included in the imageside lens sub-unit.
 7. The converter lens device according to claim 1,wherein the second lens unit comprises sequentially from the objectside, wherein the image side lens sub-unit has a negative refractivepower.
 8. The converter lens device according to claim 1, wherein thesecond lens unit comprises sequentially from the object side, whereinthe image side lens sub-unit has a negative refractive power, and theconverter lens device satisfies conditional expression (2′):0.6≦f ₂₁ /f ₂₂≦10  (2′) wherein f₂₁ is a focal length of the object sidelens sub-unit, and f₂₂ is a focal length of the image side lenssub-unit.
 9. The converter lens device according to claim 1, wherein thethird lens unit has a positive refractive power.
 10. A photographingsystem comprising: a master lens device; a camera body including animage pickup sensor; and the converter lens device according to claim 1attachable between the master lens device and the camera body, whereinan optical system constituted by the master lens device and theconverter lens device forms an image of an object, and the image pickupsensor is disposed at an image position of the object and converts animage of the object into an electric signal.
 11. A converter lens deviceaccording to claim 1, wherein the first lens unit comprises a positivelens convex to an image side, wherein a total number of positive lensesincluded in the first lens unit is one, the second lens unit comprises acemented triplet lens and a cemented doublet lens, wherein the cementedtriplet lens has a bi-concave negative lens, a bi-convex positive lensand a negative lens, and wherein the cemented doublet lens has apositive lens and a negative lens, wherein a total number of lenses inthe second lens unit is five, and the third lens unit comprises anegative lens and a positive lens, wherein a total number of lenses inthe third lens unit is two.
 12. A converter lens device comprising: afirst mount to which a master lens device is attached; a second mount towhich a camera body is attached; and a converter lens having a negativerefractive power, wherein, a focal length, in which the converter lensand the master lens are combined, is longer than a focal length of themaster lens, the converter lens comprises sequentially from an objectside, a first lens unit of a positive refractive power, a second lensunit of a negative refractive power, and a third lens unit, and thesecond lens unit comprises sequentially from the object side, an objectside lens sub-unit having a negative refractive power, and an image sidelens sub-unit having a negative refractive power, and the converter lensdevice satisfies conditional expression (2):1.7≦f ₂₁ /f ₂₂≦18  (2) where the object side is a side closer to thefirst part, an image side is a side closer to the second mount, f₂₁ is afocal length of the object side lens sub-unit, and f₂₂ is a focal lengthof the image side lens sub-unit.
 13. The converter lens device accordingto claim 12, wherein the converter lens device satisfies conditionalexpression (1):0.1≦|f|/(β×D)≦0.87  (1) wherein f is a focal length of the converterlens, β is a magnification of the converter lens, and D is a thicknessof the converter lens on an optical axis.
 14. A converter lens devicecomprising: a first mount to which a master lens device is attached; asecond mount to which a camera body is attached; and a converter lenshaving a negative refractive power, wherein, a focal length, in whichthe converter lens and the master lens are combined, is longer than afocal length of the master lens, the converter lens comprisessequentially from an object side, a first lens unit of a positiverefractive power, a second lens unit of a negative refractive power, anda third lens unit, and the second lens unit comprises sequentially froman object side, an object side lens sub-unit having a negativerefractive power, and an image side lens sub-unit having a negativerefractive power, each of the object side lens sub-unit and the imageside lens sub-unit comprises a cemented lens, and the converter lensdevice satisfies conditional expression (2′):0.6≦f ₂₁ /f ₂₂≦10  (2′) where the object side is a side closer to thefirst mount, an image side is a side closer to the second mount, f₂₁ isa focal length of the object side lens sub-unit, and f₂₂ is a focallength of the image side lens sub-unit.
 15. A converter lens devicecomprising: a first mount to which a master lens device is attached; asecond mount to which a camera body is attached; and a converter lenshaving a negative refractive power, wherein, a focal length, in whichthe converter lens and the master lens are combined, is longer than afocal length of the master lens, the converter lens comprisessequentially from an object side, a first lens unit of a positiverefractive power, a second lens unit of a negative refractive power, anda third lens unit, and the second lens unit comprises sequentially fromthe object side, an object side lens sub-unit having a negativerefractive power, and an image side lens sub-unit having a negativerefractive power, each of the object side lens sub-unit and the imageside lens sub-unit has a cemented lens, and a surface of the object sidelens sub-unit closest to the object side and a surface of the image sidelens sub-unit closest to the object side have their concave surfacesfacing the object side, where the object side is a side closer to thefirst mount, an image side is a side closer to the second mount.
 16. Aconverter lens device comprising: a first mount to which a master lensdevice is attached; a second mount to which a camera body is attached;and a converter lens having a negative refractive power, wherein, afocal length, in which the converter lens and the master lens arecombined, is longer than a focal length of the master lens, theconverter lens comprises sequentially from an object side, a first lensunit of a positive refractive power, a second lens unit of a negativerefractive power, and a third lens unit, and the second lens unitcomprises sequentially from the object side, an object side lenssub-unit having a negative refractive power, and an image side lenssub-unit having a negative refractive power, a surface of the objectside lens sub-unit closest to the object side has its concave surfacefacing the object side, and the image side lens sub-unit comprises acemented lens composed of three lenses, where the object side is a sidecloser to the first mount, an image side is a side closer to the secondmount.
 17. A converter lens device comprising: a first mount to which amaster lens device is attached; a second mount to which a camera body isattached; and a converter lens having a negative refractive power,wherein, a focal length, in which the converter lens and the master lensare combined, is longer than a focal length of the master lens, theconverter lens comprises sequentially from an object side, a first lensunit of a positive refractive power, a second lens unit of a negativerefractive power, and a third lens unit, and the second lens unitcomprises sequentially from the object side, an object side lenssub-unit having a negative refractive power, and an image side lenssub-unit having a negative refractive power, the image side lenssub-unit comprises a cemented lens composed of three lenses, and theconverter lens device satisfies conditional expression (4):−2.0≦(r _(21f) +r _(21r))/(r _(21f) −r _(21r))≦2.0  (4) where the objectside is a side closer to the first mount, an image side is a side closerto the second mount, r_(21f) is a radius of curvature of a surface ofthe object side lens sub-unit closest to the object side, and r_(21r) isa radius of curvature of a surface of the object side lens sub-unitclosest to the image side.
 18. A converter lens device comprising: afirst mount to which a master lens device is attached; a second mount towhich a camera body is attached; and a converter lens having a negativerefractive power, wherein, a focal length, in which the converter lensand the master lens are combined, is longer than a focal length of themaster lens, the converter lens comprises sequentially from an objectside, a first lens unit of a positive refractive power, a second lensunit of a negative refractive power, and a third lens unit, and thesecond lens unit comprises sequentially from the object side, an objectside lens sub-unit having a negative refractive power, and an image sidelens sub-unit having a negative refractive power, the object side lenssub-unit comprises a cemented lens, and the third lens unit comprises acemented lens, where the object side is a side closer to the firstmount, an image side is a side closer to the second mount.
 19. Aconverter lens device comprising: a first mount to which a master lensdevice is attached; a second mount to which a camera body is attached;and a converter lens having a negative refractive power, wherein, afocal length, in which the converter lens and the master lens arecombined, is longer than a focal length of the master lens, theconverter lens comprises sequentially from an object side, a first lensunit of a positive refractive power, a second lens unit of a negativerefractive power, and a third lens unit, and the first lens unitcomprises a cemented lens, the second lens unit comprises sequentiallyfrom the object side, an object side lens sub-unit having a negativerefractive power, and an image side lens sub-unit having a negativerefractive power, and the image side lens sub-unit comprises a cementedlens, where the object side is a side closer to the first mount, animage side is a side closer to the second mount.
 20. A converter lensdevice comprising: a first mount to which a master lens device isattached; a second mount to which a camera body is attached; and aconverter lens having a negative refractive power, wherein, a focallength, in which the converter lens and the master lens are combined, islonger than a focal length of the master lens, the converter lenscomprises sequentially from an object side, a first lens unit of apositive refractive power, a second lens unit of a negative refractivepower, and a third lens unit, and the second lens unit comprisessequentially from the object side, an object side lens sub-unit having anegative refractive power, and an image side lens sub-unit having anegative refractive power, the image side lens sub-unit comprises acemented lens, and the converter lens device satisfies conditionalexpression (8):−2.4≦f ₃ /f≦−75  (8) where the object side is a side closer to the firstmount, an image side is a side closer to the second mount, f₃ is a focallength of the third lens unit, and f is a focal length of the converterlens.
 21. A converter lens device comprising: a first mount to which amaster lens device is attached; a second mount to which a camera body isattached; and a converter lens having a negative refractive power,wherein, a focal length, in which the converter lens and the master lensare combined, is longer than a focal length of the master lens, theconverter lens comprises sequentially from an object side, a first lensunit of a positive refractive power, a second lens unit of a negativerefractive power, and a third lens unit, and the first lens unitcomprises a cemented lens, the second lens unit comprises sequentiallyfrom the object side, an object side lens sub-unit having a negativerefractive power, and an image side lens sub-unit having a negativerefractive power, and the converter lens device satisfies conditionalexpression (8′):−2.4≦f ₃ /f≦−1.0  (8′) where the object side is a side closer to thefirst mount, an image side is a side closer to the second mount, f₃ is afocal length of the third lens unit, and f is a focal length of theconverter lens.
 22. A converter lens device comprising: a first mount towhich a master lens device is attached; a second mount to which a camerabody is attached; and a converter lens having a negative refractivepower, wherein, a focal length, in which the converter lens and themaster lens are combined, is longer than a focal length of the masterlens, the converter lens comprises sequentially from an object side, afirst lens unit of a positive refractive power, a second lens unit of anegative refractive power, and a third lens unit, and the second lensunit comprises an object side lens sub-unit having a negative refractivepower, and a surface of the object side lens sub-unit closer to theobject side has its concave surface facing the object side.
 23. Aconverter lens device comprising: a first mount to which a master lensdevice is attached; a second mount to which a camera body is attached;and a converter lens having a negative refractive power, wherein, afocal length, in which the converter lens and the master lens arecombined, is longer than a focal length of the master lens, theconverter lens comprises sequentially from an object side, a first lensunit of a positive refractive power, a second lens unit of a negativerefractive power, and a third lens unit, and the second lens unitcomprises an image side lens sub-unit having a negative refractivepower, and a surface of the image side lens sub-unit closer to theobject side being a concave surface.
 24. A converter lens devicecomprising: a first mount to which a master lens device is attached; asecond mount to which a camera body is attached; and a converter lenshaving a negative refractive power, wherein, a focal length, in whichthe converter lens and the master lens are combined, is longer than afocal length of the master lens, the converter lens comprisessequentially from an object side, a first lens unit of a positiverefractive power, a second lens unit of a negative refractive power, anda third lens unit, and the second lens unit comprises an object sidelens sub-unit having a negative refractive power, and the object sidelens sub-unit comprises a cemented lens.
 25. A converter lens devicecomprising: a first mount to which a master lens device is attached; asecond mount to which a camera body is attached; and a converter lenshaving a negative refractive power, wherein, a focal length, in whichthe converter lens and the master lens are combined, is longer than afocal length of the master lens, the converter lens comprisessequentially from an object side, a first lens unit of a positiverefractive power, a second lens unit of a negative refractive power, anda third lens unit, and the second lens unit comprises an image side lenssub-unit having a negative refractive power, and the image side lenssub-unit comprises a cemented lens.
 26. A converter lens devicecomprising: a first mount to which a master lens device is attached; asecond mount to which a camera body is attached; and a converter lenshaving a negative refractive power, wherein, a focal length, in whichthe converter lens and the master lens are combined, is longer than afocal length of the master lens, the converter lens comprisessequentially from an object side, a first lens unit of a positiverefractive power, a second lens unit of a negative refractive power, anda third lens unit, and the second lens unit comprises an image side lenssub-unit having a negative refractive power, and the image side lenssub-unit comprises a cemented lens comprising three lenses.
 27. Aconverter lens device comprising: a first mount to which a master lensdevice is attached; a second mount to which a camera body is attached;and a converter lens having a negative refractive power, wherein, afocal length, in which the converter lens and the master lens arecombined, is longer than a focal length of the master lens, theconverter lens comprises sequentially from an object side, a first lensunit of a positive refractive power, a second lens unit of a negativerefractive power, and a third lens unit, and wherein the converter lensdevice satisfies conditional expression (1):0.1≦|f|/(β×D)≦0.87  (1) where an object side of the converter lensdevice is a side closer to the first mount, an image side of theconverter lens device is a side closer to the second mount, f is a focallength of the converter lens, β is a magnification of the converterlens, and D is a thickness of the converter lens on an optical axis,wherein the converter lens device satisfies conditional expression (8):−2.4≦f ₃ /f≦−75  (8) wherein f₃ is a focal length of the third lensunit, and f is a focal length of the converter lens.